Simulated manifold pressure system for aircraft



Oct. 8, 1957 R. G. STERN ET AL 2,808,558

SIMULATED MANIFOLD PRESSURE SYSTEM TOR AIRCRAFT 3 Sheets-Sheet l FiledJune 14, 1954 wmomgnma RcLAY Nv #bm TILT..

Oct. 8, 1957 R, G STERN ET AL 2,808,658

SIMULATED MANIFOLD PRESSURE SYSTEM FOR AIRCRAFT Filed June 14, 1954 5Sheets-Sheet 2 RB ICE SWITCH@ SHOWN WHEN E TINING MOTO. "o tAIl ICE'Q RGICI-'MAX WIT WEATHER RELAY nlitcwALl. [4.5 smrmorr www Oct. 8, 1957Filed June 14, 1954 R, G. STERN ET AL l SIMULATED MANIFOLD PRESSURESYSTEM FOR AIRCRAFT 3 Sheets-Sheet 3 United States SIMULATED MANIFOLDPRESSURE SYSTEM FOR AIRCRAFT Application June 14, 1954, Serial No.436,478

11 Claims. (Cl. 35-12) This invention relates to aircraft trainers andmore particularly to apparatus for simulating an aircraft enginemanifold pressure system of the type employing an automatically operatedtwo-stage blower and wherein manifold pressure is in the main under thecontrol of the pilots throttle lever.

- Certain types of aircraft such as those having the Air Forcedesignations C-119 and C-124 are provided with an automatic power unitwherein the pilots throttle lever functions as a manifold pressurecontrol. Manifold pressure is supplied by a two-stage blower which iscapable of operating in high or low blower for delivering more or lesspressure respectively. The manifold pressure which is actually availableat any particular time for meeting the pilots demand is dependent uponwhether the blower is operating in low or high blower, upon the altitudeof the aircraft and engine R. P. M., and upon such other factors as theextent of carburetor preheating, air filter operation, and icingconditions within the carburetor. Low blower operation prevails as longas sufficient manifold pressure is available to meet that demanded,however, when the demand cannot be met in low blower the blower isautomatically shifted into high blower operation to maintain throttlelever control of the manifold pressure. Throttle lever control of themanifold pressure becomes ineffective only if the manifold pressureavailable with the blower in high blower operation is insufiicient tomeet that demanded. A shift from low blower to high blower operation isreectced in engine oil pressure, a momentary drop in oil pressureoccurring. This drop is reflected on an oil pressure indicator and isthe main cue which the flight crew has that the blower is shifting.

Aircraft trainers of various types are well-known in the art. No trainerhas been developed however for an aircraft of the type contemplatedhaving a manifold pressure system such as described including anautomatically operated two-stage blower wherein manifold pressure isunder control of the throttle lever. It would be desirable to provide atrainer for such an aircraft for familiarizing prospective crews withthe controls and instruments of the various systems therein inparticular the manifold pressure system.

It is accordingly a prime object of this invention to provide means foreffectively simulating a manifold pressure system of the described type.

It is another object of this invention to simulate the drop in oilpressure occurring upon shifting from low to high blower operation inthe said manifold pressure system.

lIt is still another object of my invention to simulate icing anddeicing in the carburetor and the effect thereof upon the operation ofthe manifold pressure system.

Figs. l and 2 are diagrammatic illustrations which taken together showthe main components of the manifold pressure system and theirinter-relation.

Fig. 3 is a diagrammatic illustration of the .carburetor ice simulatingsystem.

` atent Fig.V 4 is a diagrammatic illustration of means for simulatingoil pressure dip due to a shift from low to high blower operation. 1

Fig. 5 is a schedule of the operation of the carburetor ice simulatingsystem.

In Fig. 1 of the drawings reference character 1 designates a simulatedthrottle lever which is connected to the slider contact 2 of apotentiometer 3. The design of potentiometer 3 is such that a voltage isderived at slider contact 2 representing manifold airpressure requested'as a function of throttle position as the throttle lever 1 is moved.This voltage is designated in the drawing as -MAPreq (throttle).Although manifold pressure requested is mainly a function of throttleposition as determined by movement of the throttle lever, the factors'of altitude and engine R. P. M. should be taken into consideration for amore accurate determination of manifold air pressure requested at anyparticular time. An altitude servo system (h) and an R. P. M. servosystem (RPM) function in computing the effect of altitude and engine R.P. M. on manifold pressure requested.

The altitude servo is typical of a number of other servo systems shownin the drawings. Other servo systems include the manifold air pressureservo (MAP), the manifold air pressure available servo (MAPv), theoutside air pressure servo (OAP), the outside air temperature servo(OAT), the carburetor air temperature servo (CAT), the oil temperatureservo (OT) and the oil pressure servo (OP). Referring to the altitudeservo system as an example, the system includes a servo amp1ier'4 towhich are applied a number of control voltages representing respectivelyquantities determining altitude as described in the co-pendingapplication of Robert G. Stern, one of the applicants in the presentapplication, for Aircraft Training Apparatus for Simulated Landing andRelated Maneuvers, S. N. 134,623, led December 23, 1949, now Patent No.2,731,737, granted January 24, 1956, and Iincludes also a motor 5responsive to the amplifier output, a feed back generator 6 driven bythe motor 5 and a number of potentiometers, as for example '7 and 8having their slider contacts connected through a gear reduction box 9 tothe motor generator set. The servo amplifier 4 is a summing amplifierfor determining the resultant for the respective input voltagesrepresenting the quantities which determine altitude. Such amplitiersare well-known in the art for algebraically `summing a plurality ofseparate A. C. voltages of Varying magnitude and polarity and a detailedcircuit illustration therefore is unnecessary.

As indicated, the output of the amplifier is used to control a servonetwork including a motor-generator set diagrammatically indicated onother parts of the drawing as M. G. The operation of the motor-generatorset is essentially the same in each of the various servos of themanifold pressure system and a single illustration for the altitudeservo is therefore suiiicient. The motor 5 is of the 2-phase type, the-control phase 10 of which is energized by the amplifier output asillustrated and the other phase 11 by a constant reference A. C. voltageel, dephased from the control voltage. The operation of this type ofmotor is well-known, the rotation being in one direction when thecontrol and reference voltages of the respective phases have the samevinstantaneous polarity, and in the opposite direction when theinstantaneous polarity of the control voltage is reversed with respectto the reference voltage, the rate of rotation in both cases dependingon the magnitude of the control voltage. A generator 6 which is drivenby motor 5 is a Z-phase generator having one phase 12 energized by a 90dephased A. C. reference Voltage e2, the other phase 13 generatingaccording to the motor speed a feed-back voltage efb for purposes ofvelocity control. The motor lS also serves to gang- A32,motor-generator'33 and potentiometer 34.

3 operate through gearv reduction box 9 and suitable mechanicalconnections indicated by dotted line 14 the contacts of a potentiometersystem as for example contacts 15 and 16 of potentiometers 7 and 8, andmay also in certain servo systems operate an appropriate indicatinginstrument.

The individual potentiometer resistance elements such as units 7 and 8of the altitude servo system may be of the well-known wound card typeand are of circular or band form in practice but are diagrammaticallyillustrated inplane development for clarity. A structural arrangementthat may `be yconveniently usedfor a servo motor and potentiometercombination of the character above referred tov is shown in PatentNumber 2,431,749., issued December 2, 1947, to R. B. Brantv forPotentiometer Housing Aand ,Positioning` Structure.

It will be apparent that operation of the servo motor ineither direction'causes the gang-operated potentiometer slider contacts, such astheslider contact 15 and 16 to moveto corresponding angular positions onthe respective potentiometer elements for deriving, i. e. picking olfpotentiometer voltages depending on the respective contact position.Each potentiometer of each servo system is shaped or contoured anddesigned with suitable shunting resistances as required so that thevalue of the derived voltage at the potentiometer contact bears acertain relationship to the linear movement of the slider contactdepending upon the particular function of the potentiometer, and has 'anA. C. voltage impressed across its terminals depending as toinstantaneous polarity and magnitudealso on the function of thepotentiometer. As stated hereinbefore, the altitude servo system and theR.A P. M. servo system serve to compute the effect of altitude andengine R. P. M. on the manifold pressure requested. The R P. M. servosystem includes the amplitier 17, motor-generator set 18 and a number ofpotentiem-eters including potentiometers '19 and 20. Potentiometer 8 ofthe altitude servo is designed to provide a voltage at slider contact 16representing the effect of altitude upon manifold pressure requested.Slider contact 16 is connected by line 21 to a line amplifier 22 foramplifying this derived voltage. A transfonrner 23 is provided toeifect' a phase shift of 180. The transformer secondary is connected lbyline 24 .to the R. P. M. potentiometer which is so designed that anegative voltage designated -AMAPreq (h, RPM) is derived at its slidercontact 25 representing theeffect of both altitude and R. P. M. onmanifold pressure requested.

As shown slider contact 2 is connected to a thyratron 26 over lines 27and 28 and slider contact 25 is connected to the thyratron over lines 29and 30. The thyratron is labeled as the critical altitude thyratron forreasons which will hereinafter become apparent. Thyratron 26 as shown isconnected with a relay 27' which includes contacts 28 and 29. The relaypicks up whenever the thyratron is operative. The thyrat'ron which isshown Ydiagrammatically for simplicity may be connected in circuit in aconventional manner, i. e. by connecting input lines 28 and 30, and theinput line 49 through their respective summing resistors to the controlgrid of the tube. The relay 27 may be connected in the plate circuitwhich is supplied with the A.Y C. voltage E.

`Slider contacts 2 and 25 in addition to being connected to the criticalaltitude thyratron are .also connected to a manifold pressure servosystem including servo amplier 'Slider contact Z'is connected over line27, line 31, back contact 28b of relay 27, line 3S, back contact 36b ofa windmilling relay 37 and line 35' to amplifier 32, providing relays 27and 37 are tlc-energized. Slider, contact 2S is connected over line 29,line 38, back contact 291; of relay 27, line 39, back contact 4Gb ofrelay 37 and line 39'V to -ampliiier 32 `provided the relays 27 and 37are deenergized. As shown potentiometer 34- has a slider contact 41connected by a line 42 to the amplifier 32 to provide an answer signaltherefor. An instrument 43 for 4 indicating manifold pressure at anyparticular time is operated by the manifold air pressure servo. Thewindmilling relay 37 is connected -by a line 44 to one end portion ofthe potentiometer 19 of the R. P. M. servo. This end portion is the onlyconducting portion of the card. The card therefore serves as a switchproviding for the energization of relay 37 only when .the slider contact45 of card 19 assumes a position along such portion. SuchV apositionifor` theslider cont-act corresponds Vto an engine R. P. M. lessthan a specified number of revolutions per minute asefg'. 400 R-. P. M.below which the engine cannot operate. When the engine R. P.'M. drops to400 revolutions perlminuteor'tlier'eatbouts the- 'throttle control leveris no longer effective in deter-mining the -manifold pres-sure. Manifoldpressure is then determined -by the outside air pressure. Simulatingmeans are provided for deriving a voltage representing outside airpressure and such means include amplifier 46 to which slider contact 15of potentiorrieter 7 in the altitude servo is connected over line 47,and transformer 48.

`ln addition to the voltages derived at slider contacts 2 and 25,-i-MA-Preq and -AMAPreq (It, RPM) resp-ectively which are .inputvoltages to the thyratron 26, there is also a negative voltage -MAPlavrepresenting in magnitude the manifold pressure :available which is fedto the thyratron `over an output line Y49 of a transformer 150. Thisvoltage is determined as the resultant of a number of factors summarizedin amplifier 151. As shown the other output line 152 of transformer 150i-s connected to front contact 28a of relay 27.

Apparatus is provided (see Fig. 2) for computing the available m-anifoldpressure in either of two stages of simulated blower operation that is,in low blower and high blower. Available manifold pressure is computedas a function of engine R. P. M. and altitude less a reduction inmanifold lpressure due to preheating of the carburetor air, airlteroper-ation and ice formation in the carburetor. Means for derivingvoltages representing the available manifold pressure as a function ofaltit-ude and'R. P. M. include R. P. servo cards 50, 51, 52 and 53, andthe altitude 'servo'card 54 in conjunction with line amplifier landtransformer S6. The potentiometer card 50 is adaptedA to provide apositive voltage at slider contact 57V representing available manifoldpressure in low yblower as a function of R. PJM. Such voltage isdesignated -f-LBMAPav (RPM). Potentiometer card 51 as shown is energizedat one end over line 58 by a negative voltage from transformer 56representing the altitude of flight in accordance with the operation ofthe altitude servo. The effect of altitude isin' this manner introducedinto the derivation of low blower manifold pressure available. The otherend of the potentiometer cardY 51 is Agrounded and the card is contoured`so that a voltage is derived atits slider contact 59 as a function ofYaltitude and IR. P. representing `an increment which whenvadrded to thevoltage -l-LBMAPav (RPM) provides a voltage quantity representing themanifold pressure available in low blower as a function of the altitude.and R. P. M. The voltage increment is designated in the drawing as-jLBiAMAPav (h, RPM). This voltage is 180 out of phase with the voltagederived at slider contact 57 of card 50 and is for this reasondesignated as a negative quantity. A voltage +HBMAPV (RPM) representingas a function o'f R. P. M. only anl increase in `rnanifoldvpressureavailable due to high blower operation is derived at the slider contact-60 of R.P. M.k potentiometer card 53, and a voltage iHBMAPav (h, R'PM)`representing an increment which when added to the quantities-l-LtBMAP'av (RPM), -LBAMAPerw V(h, RPM) and +HBMAP (RPM) produces'asumrepresenting the manifold pressure available in high blower as aAfunction of altitude 'and R, P. M. is derived at slidercontact 61 ofcard 52. Card 52 is energizednin asimilar manner to card 51, that isover Iline 5S for introducing the effectf ofaltitud-e into thederivation of the :available manifold pressure.

Slider contact 57 is connected over line 62v to manifold air pressureavailable `servo amplifier 151 and slider contact 59 is connected toservo amplier 151 over line 63 so 'that the voltages -LBMAPav (RPM) and-LBAlMAPav (h, RPM) become input voltages to the manifold air pressureavailable servo amplier. Slider contacts 60 and 61 connect with themanifold pressure lamplifier 151 only when a relay 64 which iscontrolled in accordance with the operation of a high blower thyratron65 picks up contacts 66 and 67, slider contact 60 being then connectedover a line 68, front contact 66a and line 68 with the amplifier 151 andslider contact 6l being connected with the ampli-fier 151 over line 69,front contact 67a 'of the relay 64 and line 69.V Slider contacts 60 and61 also connect over lines 68, 68 and 69, 69 respectively with the highblower thyratron 65 when relay 64 is energized. The voltages ilHBAMAPav(h, RPM), and +HBMAPtav (RPM) thus become inputs to servo `amplifier 151and thyratron 65 whenever relay 64 closes its front contacts 66a and67a. High :blower thyratron 65 has other input voltages -t-'MAP :and-MAPav respectively representing in magnitude actual manifold pressureand available manifold pressure. The voltage -l-'MAP -is derived atslider contact 70 `of a manifold pressure servo card 71 and fed to thethyratron over line 72. The -MA'Rav voltage is fed to the thyratron 65over line 73 which connects with a negative output side of `thetransformer 150. Additional inputs to the manifold pressure servoamplifier 151 are the negative voltages -AMAPLW (CPH), -A'MA-Pav (airfilter), and -AMAPav (carb. ice) which respectively Irepresentreductions in the available manifold pressure in either high or lowblower operation due to operation of carburetor preheating means,operation of the air filter, and ice conditions in the carburetor. Thesevoltages are fed to amplifier 151 over lines 74, 75 and 76. The voltage-AMAPav (OPH) representing a reduction in the availa-ble manifoldpressure due to the operation of carburetor preheating means is derived.at slider contact 77 of potentiometer 7^8 Iaccording to the position ofthe contact as determinedby a student pilot. Operation of the airyfilter is reflected by closing front Contact v80a of the air iilterswitch which completes a circuit energized yby the -MAPav voltageextending over line 81, line 81', contact 80a, line 75 and an inputresistor of suitable magnitude to lamplifier 151. The lvoltage -MAPav(carburetor ice) is yderived at slider contact 82 of potentiometer 83,`which is `energized 'by the voltage -MAPav over line S1, slider contact82 'being operated iby an ice timing motor 84. Potentiometers 78 and 83are rboth connected at one end as shown to line 81. -The :potentiometersare thus energized by the voltage -MAPW Operation of the apparatus shownin lFigs. `l and 2 which simulates the manifold pressure system in itsbroader aspects is -initiated by movement of the simu lated throttle 1.Voltage -l-MAiPreq (throttle) is derived at slider contact 2 of thepotentiometer 3 according to movement of throttle 1 and fed to themanifold air pressure servo amplifier 32 over line 27, line 31, contact281), line 35, contact 36b, and line 35 provided relays 27 and 37 arede-energized. The voltage -AMAPreq (h, RPM) derived at slider Contact ofpotentiometer 20 is also fed to the -manifold pressure servo amplier 32over lines 29, line 38, contact 29h, line 39, contact 4Gb, and line 39'provided the relays 27 and 37 are delenergized. As previously stated,voltage -l-MA'Preq (throttle) represents manifold pressure as a functionof the throttle position and the voltage -AMAPreq (lz, RPM) representsthe effects of altitude R. P. M. The voltage -AMAPreq (h, RPM) isrelatively small as compared to the Voltage -f-MAPreq .(throttle) andthe 'operation of the MAP servo is therefore in the main a Afunctiononly of the throttle position assuming there is suflicient manifoldpressure available to meet that requested in accordance with theposition of the throttle lever.

The voltage +MA-Preq {(throttle) and -AMAPreq (h,` RPM) are also -fed-to the critical altitude thyratron 26 along with the voltage -MAPIavrepresenting the available manifold pressure in either high or lowIblower operation as the case may Ebe. The critical altitude thyratronV26 is biased to yfire when the summation of the voltages e-AIMAPreq (h,RPM) and -HMAPreq (throttle) is equal to or greater than the availablemanifold pressure voltage -MAPW When the critical altitude thyratron 26is tired relay 27 picks up opening contacts 28h and 2911, and closingcontacts 28a and 29a thereby removing the voltages +M=APreq (throttle)and AMAPreq (h, RPM) as inputs to the MAP servo ampliiier 32 andsubstituting ltherefor the manifold air pressure available voltage-l-MAPav. This is accomplished by connecting -l-LMAPav voltage appearingin output line 152 of -transformer150 over front contact 28a to the MAPservo ampliiier and 'by connecting line 39 through front contact 29a toground. Accordingly, th-e MAP servo and the indicator 43 is operated atlsuch time in accordance 'with the availf .able manifold pressurer-ather than according to the pos-ition of the throttle control lever 1.As previously pointed out, windmilling relay 37 picks up whenever theengine R. P. M. becomes so low that the engine can no longer function.When this occurs, contacts 3617 and 40b open and contacts 36a and 40aclose to connect a voltage output -i-OAP of transformer representingambient air pressure to the MAP servo amplifier 32 after rstdisconnecting other -input voltages thereto. The MAP servo and indicator43 is therefore operated in such event according to the outside airpressure.

The amount of available manifold pressure represented by the term MAPavwhich is fed to the critical altitude thyratron 26 as a negative voltageover ilne 49 is dependent upon whether high or low blower operationprevails. In low blower operation the high blower thyratron 65 is unred(Fig. 2), the relay 64 is die-energized and its back contact 66h and 67bare closed. With back contacts 66h and 67b closed, line 68' and 69 areconnected to ground and the only inputs to the MAPv available servoamplier are the voltage quantities -l-LB MAPav (RPM), -LB MAPW (l1,RPM), -AMAPav (CPH), -AMAPav (air filter), and -MAPav (carb. ice) whichare fed to the amplifier over lines 62, 63, 74, 75 and 76 respectively.These quantities are summed in the MAPav servo amplifier and provideoutput voltages for the transformer 156 representing the availablemanifold pressure in low blower operation. In high blower operation, thehigh blower thyratron is fired and relay 64 is picked up: Back contacts66b and 67b are opened and front contacts'66a and 67a are closed.Accordingly, both the voltage -l-HB MAPav (RPM) and iHB MAPtw (h, RPM)are connected to the MAP servo amplier 151. The voltage HB MAPev (RPM)is connected to the MAP servo amplifier 151 over line 68, front contact66a and line 68, and the voltage :1 -HB MAPav (h, RPM) is connected toamplifier 151 over line 69, front conta-ct 67a and line 69. Thesevoltages are additional to those fed to the MAP servo amplifier in lowblower operation and provide an output for the transformer 150representing in magnitude the available manifold pressure in high bloweroperation. Input voltages -i-MAP and -MAPav are fed to the high blowerthyratron 65 regardless of whether the system is operating in high orlow blower. These two quantities represent the only inputs to the highblower thyratron in low blower operation. There are, however, two otherinput voltages to the high blower thyratron, namely |HB MAPev (RPM) andiHB MAPev (h, RPM) when the system is operating in high blower and relay64 is picked up. At such time, voltage iHBAMAPav (h, RPM) is connectedto the high blower thyratron over line 69, front contact 67a of relay 64and line 69', whereas the voltage -l-HB MAPv (RPM) is connected to thehigh blower thyratron over line 68, front contact 66a and line 68.

The high blower thyratron is biased to re whenever the manifold airpressure represented .by the voltage quantity -i-MAP attains a valuewhich is slightlyless than the' magnitu" eef-"the available manifoldpressure `-iiipiit manifold air"`pressu'r`e'yoltage `-}-MAP` attainsYsuch- 1 value'the high blower thyratron iire'st'o add the voltages-i-HB MAPs'v7 (RPM) and l-HB AMAPHN` (11,RPM) 'as input/to the 'servoamplifier ll'and thereby effect an increase in 'the output voltage oftransformer 1h50 so that such output voltage represents the manifoldlpressure available'in high blower. The voltage input 'MAPav to the highblowerthyratron accordingly increases. The input :voltages-PHE MAP(RPM), HB MAP@ (h, RPM) 'and -MAPav sum upto the available manifoldpressure in low` vblower and 'the high blower thyratron thereforeremains operative. Since the high blower thyratron tires toeffect anincrease'in the available manifold pressure `wheneverthe actual manifoldpressure -l-MAP, as determined by the voltage quantities -i-MAPn-,q(throttlc),` 'AMAPreq (It, RPM) attains avvalue slightly'less than themanifold pressure available, the critical altitude thyratron having-i-YMAlreq (throttle), -AMAPreq (it, RPM), and' -MAPav as voltage inputsis normally unlired in low blower operation. Normally, the MAP servo istherefore operated except for the minor effects of altitudeandfRL P. M.in accordance with the position of throttle lever 1 through4 low bloweroperationv and in high blower 'operation until the manifold pressureavailable in high blower 'operation is no longcr'available to meet thatrequested due to increased altitude of flight at which time the criticalaltitude thyratron fires andthe MAP servo is operatedl according to theavailable manifold pressure.` The critical autitude thyratron may befired only `transiently when the s'imilator is operated in low blower.

Thepotentiometer 83 for. deriving the voltage AMAP (carbl'ice)"h'asVits. slider contact 82 controlled by the carburetor'icfe timing motor 84which in turn is controlled by apparatus'shown inFig. 3'for Simulatingthe formation of iee inthe carburetor of `the aircraft. The formation ofice in the carburetor isY dependent upon carburetor Yair temperature,humidity and whether or not air is liowing through the carburetor.Carburetor air temperature in turn 'is dependent upon the outside airtemperature, the altitude of'fiight, and adjustment of carburetorheating means, A carburetor air`teinperature servo is provided forsiihulatin'g'air temperature conditions in the carburetor; Thecarburetor air temperature servo'is controlled by a simulated pilotcarburetor'heat control and an outside ai'rtemperature servo, and theoutside air temperatt'lfre ser'yo'is in`tu`rn controlled in accordancewith the operation of fthe altitude servo and an instructors ambienttemperature control. The carburetor air temperature servofincludes servoamplifier. 9.0. motor generator set 91 and potentiometer 92 rwithitsslider Contact 9 3 which is connect'edto the amplifier 90. As. statedthe carburetor l airftemperature servo is controlledby the outside airteniperature 'servo 'and thev simulated pilot carburetor heat control.'The pilot carburetor heat control consists of the potentiometer 94 andslider contact 95 which is connected tothe yamplifier 90, the positionof the slider contact 95 and therefore Vthe input voltage Vto amplifier90 beingrdeterm'ined by means ofa lever (not shown) which maybeipositioned by av pilot undergoing training .in the simulator." ATheoutside airtemperature servo includes the amplifier 96 motor'gencratorset97 and potentiometer cardf98 with' its slider`contact 99which ispositioned -by the motorgeneratorset 97 for deriving a voltagerepresentingoutside air temperature and which is connected tothe/amplifier 90 such that said voltage also becomes an inputto thecarburetor air temperature servo.

An instructors ambient'ternper'ature potentiometer 100 having a slidercontact 101 is provided for deriving one voltage input for the outsideair temperature servo amplifier 96. The derived voltage at slidercontact 101 represents outside'air temperature' at sea level and isdependent caerse upon movement of the slider contact along thepotentiometer'100. Suitable means may be provided whereby the slidercontact 101 can be positioned' by an instructor. The altitude servo isprovided with a potentiometer 102 and slider contact 103 for derivinganother input voltage to the outside air temperature servo 96, suchvoltage representing the effect of altitude in determining the outsideair temperature. This voltage is derived at the slider contact 103`which is connected to the amplifier 96.

The carburetor air temperature servo controls the operation ofV a pairof cam operated switches 104 and 105 according to simulated temperatureconditions kin the carburetor. These switches 104 and 105 in conjunctionwith a wet-weather relay 106 including front and back contacts 107a` and107]?, windmilling relay 37, and cam operated limit switches 108 and1709- control the energization of circuitry which includes windings 110and 110 o f the ice motor in such a manner that the motor is operated tosimulate ice conditions within the carburetor of the plane. Switch 104includes contacts 112:1V and 11211K, and switch 1 05 includes contacts114s.' and 114b. The switchesiare operated in accordance with theoperation of the carburetor air temperature servo in such a manner thatfront contact 11241 is closed only when simulated carburetor air.temperature is greater than -l0 centigrade, andv contact 114:1 is closedonly when the carburetor airV temperature is greater than +10"centigrade. Switch 108 includes contacts 149:1 and 149b and switch 109includes contacts 151a and 151b. The switches 108 and 109 are operatedby the timing motor such that contact150b is open whenever the motorarmature occupies one of two possible limiting positions andcontactlflb:QisJopenonly when the motor armature occupie'sY the otherlimiting position. The one limiting position in which contact 150b isopen corresponds to a position for slider contact. 82 (Fig. 2) atthe endofpotentiometer 83 connected vn'th'ground such that zero voltage isderived at contact 82. indicating the absence of iceV fromA thecarburetor. The other limiting position ingwhichicontact 149k is opencorresponds to a position for the. slider contact at the end ofpotentiometer 83 connected to transformer V150 such that a maximumvoltage "is" derived at contact 82 indicating maximum ice formationwithin the` carburetor,` As shown relay 106 is controlled overa circuitconnected at one end to a positive directvoltage E (D. C.) and connectedat its other end to-ground provided a contact 11112 interposed in thecircuit isclosed.) Contact 1171b may be opened and closed bytheoperation of an icing wet weather switch 111' undercontrol of -aninstructor. When the Wet weather switch 111 is in a dry position contact111b is open, the relay 106 is cle-energized, contact 1071; is open andcontact 107,41 is.closed. However when the wet weather switch 111"is inaxwet position contact 111b is closed, the relay. 106 is energized,contact 107a is open and contact 107b. is closed. Thevapparatus of Fig.3 closely simulates .theformation of ice of theplane as a function ofcarburetor air temperature, R. P. M., and atmospheric humidity. Aschedule indicating icing conditions in the carburetor as a functionofthese factors is shown in Fig. 5 ofl the drawings.

Referring toFigs, 3 and `5, wthen theinstructors icing humidity switch111 is in a dry position the wet weather relay 106 is .de-energized. andcontact 107.b is closed so 7- that a circuitis completed through thecoil 110 of the ice motor contact 149bof switch 108 (assuming there isice in the carburetor) and contact 10717. By reason of the.

both carburetor air-temperature and. of R. P. M.

When the icing humidity switch 111 is in a wetfposi tion a numberof-.things may occur depending upon4 the Such operation of the motorwith the icing .humidity switch in a dry position is independent of- 9.v simulated carburetor air temperature and engine R. P. M. The variouspossibilities are set forth in the'lastfour columns of the schedule inFig. 5. If the `simulated carburetor air temperature is less than C.,the motor will remain inoperative indicating no change in ice conditionsregardless of engine R. P. M. since neither of the motor windings willbe energized. A circuit cannot be completed through winding 110 sincecontact 10712 is open and a circuit cannot be completed through winding110 since switch 104 has its contact 112a open. The icing motor alsoremains inoperative with the ice humidity switch in the wet position ifthe carburetor air temperature is within the range of 10 C. to |10 C.and the R. P. M. of the engine is less than 400 since an energizingcircuit cannot be completed over winding 110 with relay contact 107bopen and an energizing circuit cannot be completed over winding 110 withcontact 113b of relay 37 open. If, however, the R. P. M. is greater than400 the windmilling relay is de-energized and its contact 113b is closedthereby completing an energizing circuit through winding 110', contact151b (assuming less than a maximum amount of ice in the carburetor),contact 113b, 114b of switch 105, contact 112a of switch 104, andcontact 107a of relay 106 to operate the motor, and slider contact 82 ofpotentiometer 83 in a direction indicating the formation of `ice in thecarburetor. If the carburetor air temperature is greater than -{l0contact 114a of switch 105 is closed and an energizing circuit iscompleted regardless of engine R. P. M. through winding 110, contact149b (provided ice exists in the carburetor), contact 114a of switch105, contact 112a of switch 104, and contact 107a of relay 106. Themotor is thereby caused to operate slider contact S2 toward the groundedend of potentiometer 83 indicating a melting of ice in the carburetor.

Operation of the motor in one direction or the other indicating eitherthe formation or melting of ice in the carburetor is interrupted bymeans of limit switches 108 and 109 hereinabove referred to which openthe energiz? ing circuits for the motor windings over contacts 149b and151b when the motor is operated to a position respectively indicatingthe complete melting of ice in the carburetor and the formation of amaximum amount of ice. Operation of the motor may be interrupted at anyother time upon a change in conditions occurring as for f When there isa switch-over from high blower to low blower operation in the aircraftthe crew is made aware of what is occurring by a dip which occurs in theoil pressure indicator of the plane. This effect is simulated by meansof the apparatus shown in Fig. 4. Such apparatus includes the oilpressure servo (OP) having as input voltages -l-OP (RPM, OT)representingv oil pressure as a function of R. P. M. and oiltemperature, an answer signal -OP (ANS), and a voltage signal -OP (HI.BLOWER) for reflecting a switch from Ylow to high blower operation whichsignal exists only momentarily after the high Yblower thyratron fires.The oil pressure servo includes servo amplifier 120 motor generator set121 and potentiometer 122 having a slider contact 123 wlhich connectswith the servo amplifier 120 for providing the answer signal. As stated,the oil pressure servo amplifier has an input voltage quantity -OP (RPM,OT) representing oil pressure as a function of R. P. M. and oiltemperature. Such input voltage is derived in accordance with theoperation of the R. P. M. servo and an oil temperature servo OTcontrolled as shown inthe The timing motor is selected so (impendingYapplication of Y-Stern and' Port,v the former of whom' is one of theapplicantsin the present application, for Simulated Oil Cooling Systemfor Aircraft Engine,V S.V :611,436.53 l, filed June '14, 1954 (of evendate). The R. P.jM.Vs/ervo includes a potentiometer card 124 and sliderYcontact 125, and the oiltemperature servo includes servo amplifierV126, n motor generatory set 1,27, potentiometerpcard 123 and slidercontact 129. A voltage is derived at Vslider contact 125 in the R. P. M.servo and fed to yone end ofthe potentiometer card 12S of the oiltemperature (servo suchthat voltage -I-KOP (RPM, OT) derived at slidercontact,129 of the oil temperature servo .represents the '.oil pressurein accordance with R. P. M. and oil.tenlperatureV conditions. As shown,sliderjcontact 129.connects with `the servoamplifier 120 over line`129,contact 131b andline 148 provided relay 130 is cle-energized and, itsback kcontact 13lb is closed which is normally the case. 'Theoilpressure lservo is operated in accordance withV the voltage l-OP (RPM,OT) to control an indicator 132 for reflecting R. P. M. and oiltemperature position. In low blower operation the voltage input -OP (HI.BLOWER) to the oil pressure servo is zero, the line 133 being groundedover relay contact 134b of the high blower thyratron 165 line 147 andacontact 146 of a blower shifting relay 136. When, however, there is ashift from low blower operation to high blower operation, the highblower thryratron res causing relay 64 to pick up thereby openingcontact 134b and closing contact 134a. Contact 13511 of relay 64 alsoopens and contact 135a closes. As shown line 137 connects through thecoil of relay 136 with direct voltage source E (D. C.). A momentarysurge of current is therefore produced in line 137 through condenser 138causing relay 136 to pick up whereupon contact 135b opens and contact135:1 closes thus completing a circuit through contact 139b of relay130, contact 146a of relay 136, contact 134aof relay 64, and line 133 tothe oil pressure servo amplifier causing a dip in the indicator 132. Theeffect is only momentary as relay 136 drops out when the condenser 138is fully charged whereupon relay contact 14601 opens and 1,461: closesto connect line 133 to ground over contact 134a line 145 and contact146b. The relay 130 is controlled by means of a fire wall shut-offswitch 141. Normally this switch is open so that the energizing circuitfor relay 130 extending from direct voltage source E (D. C.) through therelay coil, over line 140 and contact 144a is open at contact 1446i.Relay 130 is therefore normally de-energized and its contacts 13919 and131bare closed. Fire wall shutoff switch, however, may be moved to aclosed position in which event the relay 130 is energized over line 140to open contacts 139b and 131b and close contacts 13911 and 131a. Thishas the effect of grounding-out the |OP (RPM, OT) voltage and -OP (HI.BLOWER) voltage inputs to servo amplifier 120 so that the oil pressureservo and its indicator 129 run to a zero reading to reflect a completeremoval of pressure in the oil pressure system. As stated, the lire wallshut-off switch 141 is normally in an open position so that relay 130 iscle-energized. T he switch is moved to a closed position only when anemergency condition exists making it necessary to cut-off oil pressurein the engine.

It should be understood that this rinvention is not limited to specificdetails of construction and arrangement thereof herein illustrated, andthat changes and modifications may occur to one skilled in the artwithout departing from the spirit of the invention.

What is claimed is:

l. In aircraft training apparatus having computing means responsive tothe operation of simulator controls by a student for simulating flightconditions and aircraft operation, means for simulating the operation ofa manifold pressure system of the type having a two stage blower whichautomatically shifts from a first stage of low blower operation to 'asecond stage of high blower operation' toincrease engine manifoldpressure reqied comprising a simulated throttle` control, meansoperatively connected withsaid cont'el for deriving a voltagerepresenting manifold pressure requested accord ing tothe position ofsaid ccntrol, means for deriving another voltage opposite insign fromsaid one voltage and representing a reduction in manifold pressure refquested according rto the altitude of simulator flight and simulatedengine R. P. M., a servo mechanism having said one and another derivedvoltages as inputs thereto, indicating means operated by said servomechanism for representing manifold pressure, means for deriving avoltage representing available manifold pressure in one or the otherstages of operation of said blower including control means forregulating such derived voltage to represent available manifold pressurein low blower operation provided manifold pressure remains less than anamount which is slightly'les's than the manifold pressure which isavailable in low blower operation and to represent" available manifoldpressure in high blower if manifold pressure Veitceeds such anicunt, andmeans for disconnecting said one and another derived voltages asinputsto the servo mechanism and kconnecting thereto the voltagerepresenting available manifold pressure when the sum of the saidone andanother voltages attains a value equal to the voltage representingmanifold pressure available.

2. The aircraft training apparatus having computing means responsive tothe operation of simulator controls by a studentffor simulating flightconditions and aircraft operation, means for simulating the operation ofa manifold pressure system of the type having a two stage blower whichautomatically shifts from a first stage of low blower operation to asecond vstage of high blower operation to increase engine manifoldpressure as required comprising a simulated throttle control, meansoperatively connected with said control for deriving 'a voltagerepresenting manifold pressure requested according to the position ofsaid control, means for deriving another'voltage opposite in signfromsaid one voltage and representing a reduction in manifold pressure'requested according to the altitude of simulator flight and simulatedengine R. P.`M., a servo mechanism having said one and another derivedvoltages as inputs thereto, indicating Vmeans operated by said servomechanism for representing manifold pressure, means for deriving avoltage representing available manifold pressure in one or the' otherstages of operation of said blower including a vthyratron for regulatingsuch derived voltage to represent available manifold pressure in low orhigh blower according to whether the thyratron is unnred or firedrespectively andmeans for controlling the thyratron to hre only whenmanifold pressure 'exceeds a value slightly less than the manifoldpressure which is available in low blower operation, and means fordisconnecting said one and another derived voltages as inputs to theservo mechanism andconnecting thereto the voltage representing availablemanifold pressure when'the sum of said one and another voltages attainsa value equal to the voltage representing manifold pressure available.

3. In Iaircraft training apparatus having computing means responsive tothe operation 'of simulator controls by a student for simulating nightconditions and aircraft operation, means for simulating the operation ofa manifold pressure system of the type having a two -stage blower whichautomatically shifts from anrst stage of Vlow blower operation to asecond stage of high blower operation to increase engine manifoldpressure as required comprising a simulated throttle control, meansoperatively connected with said control for deriving a voltagerepresenting manifold pressure requested according to the position ofsaid control, means for deriving another voltage opposite insign fromsaid one voltage and representing a reduction in manifold` pressurerequested according to .the altitude of simulater flight andsimULated'engineR. P. M., a servo mechanism'having said one and anotherderived volt-ages as in- V12 v putsthereto, indicating meansoperated 'bysa id servo ine "h'anisnifdr represen't'ingv manifold pressure, meansfor derivinga vdltage epesenting'-1available manifold pressure infiievor the other stages of operation of said blower including a'thyraftlron for regulating such derived voltage torepresent',avilable'nianifold pressure in low or high blower' according'to whether the thyratron is unred or fired respectively, meansoperatively connected to said servo' viiiecharii'srri fr deriving avoltage representing nianifoldfpressurdfand means for calculating avoltage representing manifold pressureavailable in low blower operationregadlessfof whether low blower or high bloW'pratio prevails, thethyratron being operated according to the relative magnitudes of thevoltage representing.manifpldfpressure and the calculated voltagerepresenting`- manifold pressure avail-able in lower blower operation,ahdsaid th'yrat'rn being biased to 're only when the voltageepresentin'g manifold pressure exceeds a value slightly` less"th nthe`said calculated voltage, and means gone and'another derived voltagesas inputs to the seri/'o 'mechanism and connecting thereto the voltagerepresenting ava ilable' manifold pressure whenthesumof'said oneandanother voltageattains a value equal to the voltage representingmanifold pressure available.

' 4; In aircraft training vapparatus having computing means responsiveto the operation of simulator controls by a student for 'simulatingliight conditions and aircraft operation, means 'fofr mulatingthe loperation of a manifold pressuresysternpf'the type having a twostage blower which automatically shifts from a first stage of low bloweroperatiohto' a' second stage of high blower operation to increase enginemanifold pressure as required comprising asinulated throttle control,means operatively connected with said control forlderivingavoltagerepresenting manifold pressure requestedaccording to the position ofsaid control, means for deriving another voltage opposite in sign froms'aidione'voltageand representing a reduction inmanifoldipressure'requested according to the altitude of simulatorflight and simulated engine R. P. M., a servo mechanism having saidjone'and another derived voltages as'inputs'tlieetonndicating means operatedby said servo mechanism forrepre'sentin'g Irnanifold pressure, meansoperatively connected to said servo` mechanism for deriving a voltagerepresentig manifold pressure, means for deriving aliir'st: 'cl secondset of voltages, said first set representing' in` initiation availablemanifold pressure in low blower'op ation-Tas -a function of simulatoraltitude and simulated 'engine R. P.M.,' and the second set of voltagesrepresenting f n "summation with the first set available manifoldpre'ssu'reinihigh blower operation as a function of simulator 'altitudeand 'simulated engine R. P. M., summingfneans having the first set ofvoltages connected lthereto as inputs'to provide'a voltage outputrepresenting avail-able manifoldvpre'ssurein low` blower operation, thesecond set of voltages also'being 'connected to the sum mingm'eansonlyin high vblower -operation'to provide a voltage output-representing'available manifold pressure in high blowerperation, a thyr'atron havingthe second set of voltages as inputs in high blower oper-ation only'andhaving the"o'l1tpu't= voltage of t` h e summing means being oppositeinsignto the snm of said second set of voltages Wherebythe'siimofIs'u'ch Einput voltages -to the thyratron always represents theiavailable manifold pressure in low blower `operation,"the` 'thy'rat'ron'also having said voltage representing manifoldlair pressure as an inputand the thyratronbeingbiased to iir'ev so as to simulate a shift fromlow to 'high blower operation when the voltage repfesentinge'nginemanifold pressure eitceeds a value slightly less th-an"the`-summation'of 'voltages representing manifold pressure available in 'low' blower,and means controlled by said thyr-atron for connecting the Isaid secondset of voltages'to the summing mean'sand thyratron when thetliyratronres.

v5. Thecrnbinationias" definedin claim 4 with'the a'ddition of means forf'deriving rvoltages 'representing the effect l13 of air filteroperation, carburetor icing conditions and the extent of carburetorpreheating on available manifold pressure, such voltages being connectedto the summing means to more accurately determine the output voltagethereof representing available manifold pressure in either low or highblower operation.

6. The combination as `defined in claim with the addition of an oilpressure servo for registering simulated oil pressure controlledaccording to simulated engine R. P. M., and oil temperature, anindicator operated by the oil pressure servo for representing oilpressure, and means responsive to the operation of said thyratron forsupplying a temporary signal to said oil pressure servo when thethyratron fires to effect a dip in the oil pressure indicator.

7. In aircraft training apparatus having computing means responsive tothe operation of simulator controls by a student for simulating ightconditions and aircraft operation, means for deriving voltagesrespectively representing outside air temperature during the course ofsimulator flight and the extent of carburetor heating, servo meanshaving said voltages as inputs and operated thereby to reflectcarburetor air temperature, circuitry including contacts controlled bysaid servo means and positioned according to carburetor air temperatureas determined by the input voltages to the servo means, said circuitryalso including a contact controlled by an instructor for simulating wetor dry weather, an icing motor having windings energized by saidcircuitry according to the operation of said contacts to reectcarburetor icing conditions, and means controlled by said motor forderiving a voltage representing the extent of ice formation.

8. In aircraft training apparatus having computing means responsive tothe operation of simulator controls by a student for simulating ightconditions and aircraft operation, means for deriving voltagesrespectively representing outside air temperature during the course ofsimulator ight and the extent of carburetor heating, servo means havingsaid voltages as inputs and operated thereby to reect carburetor airtemperature, circuitry including cam-operated contacts controlled bysaid servo means and positioned according to carburetor air temperatureas determined by the input voltages to the servo means, said circuitryalso including a contact controlled according to whether simulatedengine R. P. M. is less or greater than a predetermined amountrepresenting a limiting condition for operation of the aircraft engine,the said circuitry further including a contact controlled by aninstructor for simulating wet or dry weather, an icing motor havingwindings energized by said circuitry according to the operation of saidcontacts to reflect carburetor icing conditions, and means controlled bysaid motor for deriving a voltage representing the extent of iceformation.

9. In aircraft training apparatus having computing means responsive tothe operation of simulator controls by a student for simulating ightconditions and aircraft operation, and including means for simulatingthe operation of a two stage blower for supplying manifold air pressure,an oil pressure servo for registering simulated oil pressure controlledaccording to simulated engine R. P. M. and oil temperature, a D. C.voltage source, circuit means including a condenser and a relay, meansoperated to reect a shift in blower operation for one stage to anotherfor causing said circuit means to be energized by the D. C. voltagesource thereby energizing the relay through the condenser momentarilyuntil the condenser is fully charged whereupon the relay is deenergized,another voltage source, circuit means controlled by said relay toconnect said another voltage source to the oil pressure servo while therelay is energized, the oil pressure servo thereby being operated toreflect a momentary oil pressure dip, and indicating means controlled bythe oil pressure servo.

l0. In aircraft training apparatus having computing means responsive tothe operation of simulator controls by a student for simulating flightconditions and aircraft operation, means for simulating the operation ofa manifold pressure system of the type having a two stage blower whichautomatically shifts from a first stage of low blower operation to asecond stage of high blower operation to increase engine manifoldpressure as required comprising a simulated throttle control, meansoperatively connected with said control for deriving a first controlquantity representing manifold pressure requested, means for deriving asecond control quantity representing the effect of altitude and engineR. P. M. on manifold pressure requested, means for computing manifoldair pressure controlled at times according to said first and secondcontrol quantities, means for deriving a third control quantityrepresenting manifold pressure available in one or the other stages ofoperation of said blower including control means for regulating suchcontrol quantity to represent manifold pressure available in low andhigh blower operation respectively according to the computed value ofmanifold air pressure as compared to the manifold pressure available inlow blower, and means operated according to the first, second and thirdderived control quantities for controlling the manifold air pressurecomputing means accordingto the said third derived control quantity whenthe combined value of said first and second control quantities isgreater than the third control quantity representing manifold pressureavailable.

1l. In aircraft training apparatus having computing means responsive tothe operation of simulator controls by a student for simulating flightconditions and aircraft operation, means for simulating the operation ofa manifold pressure system of the type having a two stage blower whichautomatically shifts from a first stage of low blower operation to asecond stage of high blower operation to increase engine manifoldpressure as required comprising a simulated throttle control, meansoperatively connected with said control for deriving a first controlsignal representing manifold pressure requested, means for deriving asecond control signal representing the effect of altitude and engine R.P. M. on manifold pressure requested, means for computing manifold airpressure controlled at times according to said first and second controlsignals, indicating means controlled by said computing means, means forderiving a third control signal representing manifold pressure availablein one or the other stages of operation of said blower including controlmeans for regulating such control signal to represent manifold pressureavailable in low and high blower operation respectively according to thecomputed value of manifold air pressure as compared to the manifoldpressure available in low blower, and means operated according to thefirst, second and third derived control quantities for controlling themanifold air pressure computing means according to the said thirdderived control signal when the first and second control signals insummation are greater than the third control signal representingmanifold pressure available.

References Cited in the le of this patent UNITED STATES PATENTS2,496,617 Burelbach Feb. 7, 1950 2,499,597 Lukacs Mar. 7, 1950 2,506,949Burelbach et al May 9, 1950 2,510,500 Hayes et al. June 6, 1950

